In radio-based communication networks, intermediate transport networks may be used to convey data between different nodes of the communication network. One example of such a scenario occurs when using high speed packet access (HSPA). Here, a transport network (TN), also referred to as lub transport network, may be used in the universal mobile telecommunications system (UMTS) terrestrial radio access network (UTRAN) to couple a radio network controller (RNC) to a radio access node, also referred to as radio base station (RBS) or Node B. HSPA in the direction from the communication network towards user equipment (UE) is referred to as high speed downlink packet access (HSDPA), and HSPA in the direction from the UE to the communication network is referred to as high speed uplink packet access (HSUPA).
According to HSPA, two levels of link layer retransmission protocols are used: hybrid automatic repeat request (HARQ) between the UE and the Node B, and radio link control (RLC) between the UE and the RNC. A flow control protocol, also referred to as framing protocol (FP), has been introduced to control the sending rate of the RNC in the downlink direction and the sending rate of the Node B in the uplink direction. The FP needs to address congestions on the radio link between the Node B the UE and congestions in the transport network between the RNC and the Node B, and will try to set an optimal sending rate which is as high as possible while avoiding the above mentioned types of congestion. This means that the FP attempts to control the sending rate in such a way that the fill level of queues in subsequent nodes will not exceed respective threshold sizes. HSDPA/HSUPA Handbook, Edited by Borko Furht and Syed A. Ahson, CRC Press, October 2010, Chapter 9—HSPA Transport Network Layer Congestion Control provides further information of the congestion control applicable to HSDPA and HSUPA.
However, it has turned out that the above-mentioned optimal sending rate is typically hard to achieve using the known FP. Further, typical scenarios of using HSPA involve, e.g. a rapidly changing radio capacity available to a certain RLC connections or different lub transport network deployments with different RLC round trip delays. This may result either in the sending rate being set too low or in congestions not being avoided. Both adversely affect the end-to-end performance, e.g. measured in terms of throughput.
Moreover, the known FP handles all RLC connections in the same manner. This may result in that the end-to-end performance experienced by a high-priority service or user will suffer from congestions in the lub transport network caused by RLC connections related to a low-priority service or user. The FP in HSDPA may also be configured to target fair bandwidth sharing among users or the target bitrate may be coupled to a user class so that some users get e.g. twice as much throughput as other users. In order to achieve this behavior, the HSDPA FP entity in the Node B scales the target bit rates for each flow or user so that they match the desired relative bit rates. However, this still does not solve the above-mentioned problems of adapting the sending rate.